1. Field of the Invention
This invention relates to a system which collects a specific volume of arterial or venous blood for gas analysis or standard laboratory tests.
2. Description of the Prior Art
Presently, the most widely used arterial blood gas sampling technique employs a low resistance plunger type syringe which is heparinized prior to use in order to prevent blood clotting. The syringe is heparinized by drawing liquid heparin into it. The volume of liquid heparin necessary to adequately heparinize the syringe can cause inaccuracies in the gas analysis of the blood. For example, the heparin can introduce a change in the order of 6% to 24% in the measurement of the gas PCO.sub.2, depending primarily upon the volume of heparin which is actually used. Similarly, inaccuracies on the order of 2% to 6% in the measurement of PO.sub.2 gas levels may also be introduced when a plunger type heparinized syringe is used.
In order to overcome the problems of sample contamination caused by the use of a plunger type liquid heparinized syringe, a vacuum tube has been developed which contains a dry lyophilized heparin disc. The vacuum tube includes a seal providing stopper at one end through which a needle can be inserted. When the vacuum seal is broken, the heparin disc breaks up and coats the interior of the vacuum tube.
In general, a needle is inserted into a patient's vein or artery and a vacuum tube is then inserted over the rear end of the needle, thus breaking the vacuum seal and drawing blood into the vacuum tube. The needle and tube are usually carried within a holder and the stopper is held within the holder by means of a friction fit. Since the tip of the needle is already in the artery or vein when the vacuum tube is activated (i.e., when the vacuum seal is broken and the tube forced into flow communication with the needle), the activation must be accomplished carefully in order to prevent undesirable transection or pulling out of the blood vessel. When a vessel is transected, blood leakage into the surrounding tissue may cause a hematoma.
A further problem with the typical vacuum tube system is that it is a two step process which requires the technician to reposition his hands during sample collection. The technician uses one hand to stabilize and localize the blood vessel during insertion of the needle. After the needle is inserted, the technician must use that hand to apply the required force for activation of the vacuum tube. This removes the technician's ability to maintain the required stabilization and localization of the vessel, thus increasing the possibility of transection or pulling out.
Thus the major drawback of the above described system is that a longitudinal force, i.e., a force along the axis of the needle and vacuum tube, must be applied in order to activate the tube. This longitudinal force is generally perpendicular to the direction of the blood vessel and a slight movement can thus cause transection of the vessel. In order to overcome this problem, devices have been developed which include a valve which is actuated by the application of lateral rather than longitudinal forces. Devices of this type are disclosed in U.S. Pat. Nos. 3,143,109 to Gewertz, 3,308,809 to Cohen, Italian Pat. No. 469,055 and Italian Pat. No. 464,109. With the exception of Gewertz, all of these patents disclose unitary structures. Thus, they cannot be used with a separate vacuum tube. In one embodiment of Gewertz, the valve and tube arrangement is unitary and the needle section is detachable. This type of embodiment could not be used to obtain arterial blood samples, since the arterial pressure would force blood through the needle prior to the attachment of the valve and tube assembly. In a second embodiment of Gewertz, an integral needle and valve arrangement is provided having a cylindrical upper body portion having corrugated ridges for engaging receptacles, bottles or the like. This type of device can not be utilized with the typical vacuum tube having a rubber sealing stopper at one end since it does not contain any means of breaking the vacuum seal.